The present invention relates to image decoders which decode image signals.
Digital recorders and video cameras, available these days on the market, use MPEG or other compression techniques to digitally encode video and audio signals for storage on recording media such as hard disks (HDDs) and optical disks (DVDs). Such a recording apparatus, equipped with a plurality of recording media, for example, a HDD and a DVD, has the recording capability of recording to these media (encode process) and playback capability of playing back them (decode process). In order to allow backup or long-term storage of originally recorded data, it also has the capability of dubbing recorded data between the two media. During this dubbing, it is common to perform transcode processing in order to change the compression rate or because of different compression encoding formats assumed for the respective media. The transcode processing performs re-encoding to converts the encoded format of the original compressed video/audio signal.
For such image recording and playback techniques as mentioned above, high speed operation is needed as the case may be. For example, in the case of transcoding where decoded images are re-encoded, if both decoding and re-encoding are performed faster than real time, it is possible to reduce the time required for the transcoding. This reduces the user's waiting time and therefore improves the usability. Generally, as represented by the ISO/IEC131818-2 standard (commonly referred to as MPEG2 Video), motion images are encoded/compressed by using interframe prediction-based compression/encoding techniques. Therefore, transcoding is required to retain interframe reference relations for processing data.
For example, JP-A-2007-86487 and JP-A-2007-86488 (Patent Documents) disclose an apparatus which performs high speed decode processing by using a plurality of decode chips. According to the above-mentioned Patent Documents, the incoming MPEG stream is divided into slices or other components constituting each frame and distributed between the decode chips where decode processing is performed. In addition, reference images are mutually transferred between the chips so that each chip can use reference images created in the other chip. Thus, it is possible to perform decode processing by shortening the processing time as described therein.